Phages are viruses whose hosts are bacterial cells. The phages identify their hosts through host cell-specific receptor molecules, which are located on the outside of the host cell. Once the phages find their specific receptors, they bind to the bacterial cell and inject their nucleic acid into the cell. The phage nucleic acid then takes over the host cell's machinery to make large amounts of phage components. The phage components are then assembled into new phages. The phages then direct production of an enzyme that breaks down the bacteria cell wall, which causes the bacteria to lyse, which further frees new phages. Phage lysis assays are known in the prior art for the detection and identification of various bacterial pathogens.
Antibodies have also been used to discriminate bacterial species. However there are a number of advantages to using phage-based detection schemes, as opposed to using antibody-based schemes. More specifically, antibodies are bare protein molecules. As such, they are potential food sources for bacteria. Bacterial “grazing” of antibody-coated magnetic microparticles has been observed. Such grazing can result in false positives, when compared to a phage-based scheme. Other limitations of antibody-based immunoassays include antibody manufacturability and instability.
Each bacterial species has at least one phage that will prey upon it. Phages can be readily obtained from phage libraries. One such library is the Felix D'Herelle Reference Center for Bacterial Viruses at Laval University in Quebec, Canada. This library has a collection of approximately 500 different species of phage. Phages are very robust and are not as sensitive to environmental conditions (pH, temperature, salinity, etc.) as antibodies are. Large quantities of phages can be easily cultured and purified. Additionally, the purified phage exhibits a long shelf life relative to antibodies.
In view of the above, it is an object of the present invention to provide a device and method for detecting bacteria using fluorescently-labeled phage immobilized on an optically transparent surface that minimizes false positives. Another object of the present invention is to provide a device and method for detecting bacteria using fluorescently-labeled phage immobilized on an optically transparent surface that is stable and that can easily be stored for extended periods of time prior to use. Still another object of the present invention is to provide a device and method for detecting bacteria using fluorescently-labeled phage immobilized on an optically transparent surface that can use multiple phages at the same time, to provide for testing of multiple species of bacteria at the same time, and that can distinguish between different types of bacteria. Yet another object of the present invention to provide a device and method for detecting bacteria using fluorescently-labeled phage immobilized on an optically transparent surface that is easy to manufacture in a cost-effective manner, and that is easy to use by remote operators in the field.